Group Policy - Preferences

Using group policy there is various settings required for our users. We have been using the preferences policy located at: Administrative Templates > Mozilla > Firefox > Preferences This policy requires the use of JSON, we have been using the following which has been working ok: { "media.navigator.permission.disabled": { "Value": true, "Status": "user" }, "browser.warnOnQuit": { "Value": true, "Status": "user" }, "keyword.enabled": { "Value": false, "Status": "user" }, "browser.tabs.unloadOnLowMemory": { "Value": false, "Status": "user" }, } Within the old "Preferences (Deprecated)" there is a setting called "intl.accept_languages" which we are wanting to use but I can't seem to find a way to include this within the JSON. We are wanting to set it to "en-GB". If I enable this within the old deprecated preferences section it causes the Preferences with the JSON to stop working. I have tried various combinations of including it within the JSON but neither are working: "intl.accept_languages": { "Value": en-GB, "Status": "user" } "intl.accept.languages": { "Value": en-GB, "Status": "user" } I've checked the Mozilla website here: https://mozilla.github.io/policy-templates/ There doesn't seem to be any reference for the intl.accept_languages setting to be used within the JSON Please can someone advise?